Truhlar Group Research Snapshot of research on Oct. 2, 2003 Graduate Students Vanessa Audette Ari...
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Transcript of Truhlar Group Research Snapshot of research on Oct. 2, 2003 Graduate Students Vanessa Audette Ari...
Truhlar Group Truhlar Group ResearchResearch
Snapshot of research on Oct. 2, Snapshot of research on Oct. 2, 20032003Graduate Students
Vanessa Audette
Ari Chakraborty
Ben Ellingson
Shikha Nangia
Jingzhi Pu
Nate Schultz
Jason Thompson
Yan Zhao
Post Docs
Ahren Jasper
Hai Lin
Ben Lynch
Chaoyuan Zhu
Visiting Researchers
Keith Kuwata
8 + 4 + 1 = 13
Subgroups Kinetics
Ben E., Keith, Hai, Pu, and Yan (emeritus: Ben L.)
Nanotechnology
Ahren and Nate
Solvation (with Chris Cramer)
Ben L., Jason, and Casey Kelly
Quantum
Vanessa, Ari, Shikha, and Chao (emeritus: Ahren)
Direct DynamicsH2S + OH SH + H2O
A saddle point is found on the potential energy surface (red dot).
Using an electronic structure program (Gaussian98), the gradient is followed down the surface creating the Minimum Energy Path (blue line) by calculating the energy and gradient at every point.
-1.5
-1
-0.5
0
0.5
1
-0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40
Reaction Coordinate (bohr)
Energy (kcal/mol)
Ben E.
Direct DynamicsRate Calculation
The Vibrationally Adiabatic Ground State curve is created by calculating frequencies and adding on zero-point energy. This curve is used for tunneling calculations.
Free energy is calculated using the frequencies and other information. The optimal dividing surface is located at the maximum of free energy. In this reaction, the optimal dividing surface occurs before the saddle point (Reaction Coordinate = 0).
13.5
14
14.5
15
15.5
16
16.5
-0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40
Reaction Coordinate (bohr)
Va^G (kcal/mol)
Dynamical Study of the Reactions of OH Radical with Unsaturated Hydrocarbons
Yan
Low temperature (<500 K):
Association reaction
OH + C2H4 HOC2H4
High temperature (~500 – 1000 K):
Hydrogen abstraction
OH + C6H6 C6H5 + H2O
*Variational Transition State Theory/Multidimensional Tunneling
POLYRATE
*Direct Dynamics
*Multi-Coefficient Molecular Mechanics (MCMM)
MC-TINKERATE, …
*Multi-Coefficient Correlation Methods (MCCMs)
MCG3, MC-QCISD, …
*Hybrid Density Functional Theory
MPW1K, …
Two Reaction Channels
V
s
Loose TS
C2H4OH
HO · · · C2H4
*Variational TS Theory for Loose TS
Generalized Hybrid Orbital (GHO) method for Combining Ab Initio
Hartree-Fock Wave Functions with Molecular Mechanics
Pu
GHO Scheme
Figure 1. Schematic representation of the QM/MM division along a covalent bond and the hybrid orbitals on the GHO boundary atom B. The shaded orbital is the active hybrid orbital.
HaiMCMM: Multi-Configuration
Molecular Mechanics
ψ1 ψ2
H=ψ1 Hψ1 H12
H12 ψ2 Hψ 2
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
=V1
MM V12
V12 V2MM
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
A + BC AB + Cvalence bond configuration
molecular mechanics configuration
diabatic coupling
Choose V12 to make it accurate:Use quadratic expansion of V12
to reproduce quadratic expansion of adiabatic energy in local regions.
LEPS, Coulson
Allinger
Chang, Miller
Join local fits of V12 by Shepard interpolation. Collins
local regions
Eigenvalue is adiabatic energy. Put italltogether:
MCMM
Keith Recent experiments on 3-hexenes with vinylic deuteriums (Kroll, J. H. et al., J. Am. Chem. Soc. 2002, 124, 8518) revealsignificant production of OD radicals, perhaps due to the isomerization and
These mechanisms are under study by direct dynamics calculations.
decomposition of dioxiranes. Possible mechanisms of OD formation:
Nanotechnology Subgroup
Ahren
& Nate
MCG3/3 PBE0/MG3 PBE0/MECP-pTZ LSRGolMBMBTB-S
Aln: A range of methods for a range of sizes
7~<n 13~<n 75~<n 3500~<n 000,10>>n
Future of the Nanotechnology Group
Al381
+
CCH Al381CCH
Solvation
Ben
Jason
Solubility of High Energy Materials in Supercritical CO2
Quantum Subgroup
Ari Shikha
Vanessa
Chao
• Inclusion of anharmonic effects
• Inclusion of rotational-vibrational interactions, such as Coriolis
coupling and centrifugal distortions
Conventional method of computing partition function Q(T): Rigid-rotor Harmonic oscillator
Improving the Rigid-rotor Harmonic Oscillator model
MethodologyVariational Self Consistent Field (VSCF) method is a powerful technique
for calculating accurate rovibrational energy levels
Calculation of accurate partition functions using rovibrational energy levels Ari
Path Integral Monte Carlo Methods Vanessa
• Propagator is written as a sum over all paths
• Path integrals coupled with Monte Carlo sampling can be used to calculate partition functions
ener
gy
reaction coordinate
ground electronic state
excited electronic state
C + AB reaction
A + BC quenchingA* + BC
reaction CA B +
A CB+
quenching
A CB+
A CB
hν
ShikhaQuantum Photochemistry
Chao
Self-Consistent Decay of Mixingwith Coherent Switching for Photchemical Processes
In the strong interaction region:
Asymptotically:
However, the transition probabilities are computed coherently, yet self-consistently.
21SCDM or VVV ≈€
VSCDM ≈ Vmean. Effective potential VSCDM as a function of time.
.
reaction path
coupling
Upper diabat V1
Lower diabat V2
That’s all, folks.
FINIS